This invention is directed to a silane primer composition and, in particular, to a silane primer composition for binding a plastic material to glass or steel by a coupling reaction.
Silane primers for use in multi-layer composite molded structures are known in the art. These structures may be used in sanitaryware composite articles such as bathroom and kitchen fixtures, and particularly in bathtubs, sinks, whirlpools, and shower receptors. In U.S. Pat. No. 4,664,982, the disclosure of which is incorporated by reference herein, a multi-layer structure includes a metal substrate with a ceramic enamel layer. A silane primer is used to bind a plastic layer to the enamel layer. The preferred silane primer is specified as vinyl silane, particularly 3[2(vinyl benzylamino) ethylamino] propyltrimethoxy silane.
Another multi-layer composite molded structure is disclosed in U.S. Ser. No. 07/400,289, the disclosure of which is incorporated by reference herein. A silane primer is used to bind a plastic layer to a non-enameled portion of a metal substrate. Again, the preferred silane primer specified is vinyl silane, particularly 3[2(vinyl benzylamino) ethylamino] propyltrimethoxy silane.
Although the silane primer may be incorporated into the plastic layer and then applied to the substrate, the preferred method of application is to spray or otherwise apply the silane primer onto the enameled or non-enameled metal substrate and then apply a plastic foam material using insert-molding techniques. In order to form a bond between the silane and the enameled or nonenameled metal substrate, the silane primer should be dissolved in a diluent so that, after application onto the enameled or nonenameled metal substrate, the silane in the primer hydrolyzes with atmospheric moisture in response to the evaporation of the diluent. The diluent traditionally used for this purpose is isopropanol alcohol.
However, isopropanol alcohol is less than satisfactory as a diluent of the silane primer if the ambient temperature is high or if the ambient humidity is low. In these conditions, the isopropanol alcohol begins drying and the silane begins to hydrolyze as, or even before, the silane primer is applied to the enamel or metal substrate. If the hydrolyzation partially or completely occurs before the silane primer is applied to the enamel or metal substrate, the silane does not satisfactorily chemically bond, if at all, to the enamel or metal substrate, and delamination occurs.
Moreover, the present inventor has found a particular silane coupling agent for use in a silane primer composition which provides unexpectedly superior resistance to chipping, cracking, crazing, deformation and delamination of the multi-layer composite molded structure when the structure is subjected to impact forces of energy.
Accordingly, a silane primer composition which is effective at chemically bonding plastic to an enamelled or nonenamelled metal substrate at high temperatures and low humidity, and a silane primer composition which provides maximum resistance to chipping, cracking, crazing, deformation and delamination of the multi-layer composite molded structure when the structure is subjected to impact forces of energy is desired.